This invention relates to a fluid-to-fluid shaft seal for use in a rotary machine and, in particular, to a seal assembly wherein a high pressure sealing fluid is utilized to pressure balance one or more pressure breakdown bushings contained within the assembly to prevent the bushing from locking against the machine frame.
In many high speed, high pressure machine applications, as for example those encountered in the turbine and compressor art, the rotating machine components are mounted upon a shaft and the shaft journaled for rotation within an opening formed in the end wall of a pressurized casing. Shaft seals are typically positioned within the shaft opening. As the shaft rotates under load, it is caused to vibrate or deflect. It has been found that the deflected shaft can move the shaft seals whereby the seals become grounded against the stationary machine frame. When the seal becomes grounded, the seal responds as a journal in regard to the shaft and shares the shaft load with the bearing system. This, in turn, has a deleterious effect upon the operation of the machine and also prevents the shaft bearings from reacting effectively in response to shaft vibrations at critical operating speeds.